The present invention relates to a pipe coupling which may have the form of a divided connector for interconnecting two equal double-walled pipes or, respectively, have the form of coupling portions formed on each of the two pipes, wherein each pipe consists of two concentric pipe walls maintained circumferentially equally spaced from each other by means of spacers placed with their longitudinal direction in the direction reaction of flow. Thus, between the two concentric pipes, an inner pipe and an outer pipe, a through-going annulus exists, serving as a liquid passage and which, except from the portions being accommodated by the spacers, is coherent between the end couplings. In the portions provided with spacers, axial channels are disposed, so that liquid passage exists between the through-going annuli.
Double-walled filter pipes are, for example, used in hydrocarbon producing beds in the rock ground. Such filter pipes have longitudinal strainer elements spaced axially and serving to filter away, among other things, formation sand from the oil let into the liquid passage of the double pipe.
A production tubing string can be supplied with oil from said annulus and is, to that end, equipped with a passage, valve, or the like on a suitable place at the extent of the double-walled filter pipe, appropriately adjacent the scarf box thereof which, according to known technique, creates passage from the outer annulus-shaped, concentric liquid passage.
Upon the completion of oil and gas wells, it is often desirable to interconnect two or more such double-walled pipes. When effecting such an interconnection, one has to see to that the inner liquid passage is rectilinear and has a circular circumference, so that also mechanical accessory can pass past the coupling portions, while the outer passage only shall serve to convey liquid. Pressure drop across the outer passage should be as low as possible, and the flowing channel(s) should, therefore, be formed according to a geometry securing low resistance against flowing. It is important that the connector or the coupling portions, respectively, in case they are formed on adjacent pipe end portions, is/are not mechanical weaker than usually used pipe couplings for interconnecting pipes having a single liquid passage, as mechanical loads such as tensile stresses, torsional stresses and bending loads may be high during run-in in the well. The coupling should exhibit the same pressure performance for external and internal pressure as usually used pipe couplings for single course in respect of the inner centric pipe passage.
The internal diameter of the coupling piece/connector or of the threaded or in some other way shaped coupling portions formed at the ends of the individual pipes respectively, must correspond to the internal diameter of the connected inner pipe. The external diameter of the coupling or the coupling portions, respectively, must be smaller than the hole into which the coupling is to be placed.
Two coupling methods for interconnecting double-walled pipes having concentric, separate annulus-like liquid passages are previously known.
(A) An inner pipe is attached to an outer concentric pipe with intermediate spacers in the form of brackets or similar spacing members. In this known design, the inner pipe is at each end equipped with a sealing device entering into sealing engagement upon interconnecting the outer pipes of the double-walled pipes through screwing. In this known double-walled pipe design, the outer pipe normally accommodates all mechanical load.
(B) At each end of a number of outer pipes, an internal, smooth sealing face has been premounted. After all outer pipes have been assembled, an inner, narrower pipe is thereupon inserted, said narrower pipe having sealing devices matching the smooth sealing faces of the cuter pipes.
A coupling device according to (A) represents a relative simple solution. However, it requires that the outer pipe is in a position to accommodate all mechanical load. Therefore, this known coupling device is unfit for use in connection with the aforesaid filter pipes, the outer pipes thereof along certain portions consisting of strainer elements in the form of spun wire filter structures.
The coupling device according to (B) requires that inner as well as outer pipe are mechanically strong due to the fact that they have to carry their own weight and withstand and accommodate mechanical strains and stresses during a separate run-in. As a consequence of that, for example, valves: externally are limited to a diameter corresponding to said smooth sealing face of the outer pipe, the internal diameter of inner pipe having associated valves and similar accessory becomes smaller than desirable. Moreover, the coupling device is time-consuming to install.
Consequently, according to the present invention, one has aimed at remedying or to a substantial degree reducing deficiencies, disadvantages and restrictions of application and use adhering to known and conventional technique and, thus, providing a pipe coupling device consisting of mutually joinable, preferably screwable coupling portions formed directly on the double pipe ends or, respectively, of corresponding, mutually joinable, preferably screwable parts of a connector, said connector parts each being attachable on an adjacent double pipe end portion. In both the indicated embodiments, the coupling device allows a simple and rapid interconnection of the two double pipes, each of which exhibiting two concentric pipe walls defining an inner separate and an outer separate liquid passage. The inner pipe of the double pipe shall be the mechanically supporting double pipe portion, while handling such as lifting/lowering and interconnection shall take place through the outer surfaces. Commonly used lifting, hoisting, hanging and tightening accessory should be usable in order to mount the double pipes (filter pipes) by means of the coupling device in accordance with the invention in a water, oil or gas well. For use as a filter pipe having longitudinal strainer element in the form of spun wire structures, slits or perforations, not too strict demands should be made on the outer pipe of the double pipes in respect to its mechanical strength, because the outer pipes along a great part of their length can be constituted by the above-mentioned filter representing mechanical weakenings.
Further objects, advantages and features of the coupling device according to the invention are further explained in the following with reference to accompanying drawings showing various exemplary embodiments, and wherein: